What should I do about this?

I was in cl one day, and we weren't doing anything, so we were all standing around talking. I overheard the teacher talking about how much water she drinks, and I said for her to be careful because if you drink too much water you can cause kidney failure. Well, we debated about it, and she said that I load up my kidneys with soda and fill up on junk food (which is a blatant lie, also nobody said anything about soda except her), and then some of the students started to pick on me about my weight. I'm about 10-20 pounds overweight, and I've been loosing it, so I don't see why they're picking on me now after I've lost several pounds. In the end, I was the one who felt insulted. So later, my friend told me that he has her cl, and that she was about to cry because I am "slow," as she puts it, and I allegedly insulted her, which I didn't. Now I'm absolutely upset because she is badmouthing me and telling people I'm slow! On top of that, this is the second year in a row that a teacher has badmouthed me for something I didn't do. Last year it was a teacher that I never had/never spoke two words to. But what am I supposed to do tomorrow when I walk into her cl?